In plasma processing applications, such as the manufacture of semiconductors or flat panel displays, RF power generators apply a voltage to a load in a plasma chamber and may operate over a wide range of frequencies. Experience in the plasma-processing industry has been able to associate particular plasma parameters (e.g., ion density, electron density, and energy distribution) to characteristics (e.g., uniformity, film thickness, and contamination levels) of the processed material (e.g., wafer). In addition, a wealth of knowledge exists that connects wafer characteristics to overall quality; thus there is experience in the plasma process industry that associates plasma parameters to the quality of the overall processing.
Obtaining information about plasma parameters (e.g., by direct measurement of the plasma environment), however, is difficult and intrusive. In contrast, identifying electrical characteristics (e.g., voltage, current, impedance, power) of RF power that is applied to a plasma processing chamber is a relatively inexpensive way to obtain a large amount of information, but existing techniques for identifying electrical characteristics are either too expensive, too slow, or too inaccurate to provide a sufficient amount of information to establish a known and repeatable association between the electrical characteristics and plasma parameters.
In particular, the RF power delivered to a plasma chamber typically includes significant amounts of power at a relatively few discrete frequencies (e.g., less than 20 frequencies). Known monitoring techniques, however, analyze a broad range of frequencies (e.g., including frequencies that do not substantially affect the plasma parameters). And as a consequence, these known techniques are too slow or too inaccurate to provide a sufficient amount of information about the electrical characteristics of the relevant frequencies. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.